But of course the Earth lacks what Flannery calls a "command-and-control" system, but as he says, so do extreme complex ant colonies. They rely on pheronomes. And Flannery suggests potential substances in Gaia that act as "geo-pheronomes", which act to help maintain conditions suitable to life, including ozone, which shields life from ultraviolet rays, the greenhouses hases, which play a critical role in controllling surface temperature, and dimethyl sulphide, produced by certain algae, which assists in cloud formation. There's also atmospheric dust, much of which is organic in origin.
He sees as a vital mechanism in making this work coevolution "natural selection that is triggered by interactions between related things... it can act at every level, from that of individual amino acids to entire organisams, and it may not be just a property of life...astromers argue that black holes and galaxies develop an interdependence that's akin to biological evolution". In simpler terms, antelope have evolved to run just faster than lions (there's no advantage in running a lot faster), so lions can catch only the old and the weak. And, Flannery says, criitically, we humans and our ancestors have been co-evolving with many species of seven milion years. He gives the lovely example of the greater African honeyguide, which feeds solely on the larvae, wax and honey of beehives. When it sees a human, it akes a striking call to attract the human's attention, "then moves off, stopping frequently to ensure that the person is following it, all the while fanning its tail to display white spots that we visually oriented humans find eawsy to see. When native Africans reach a hive with the help of a honeyguide, they break it open and often thank the bird with a gift of honey." Yes, sadly says, this relationship is beginning to break down, because with cheap sugar available, humans can no longer be bothered to seek out honey. Flannery sees this as a symbol of the way we've "destroyed many coevolutionary bonds that lie at the heart of productive ecosystems".
This may have started making significant impact as much as 30,000 years ago, with our hunting to extinction of the Siberian mammoth. Today the soils are too acid and the nutritional value of the boggy plant matter too low to support much at all - reindeer survive by eating lichens rather than grass, yet a very similar environment supported an abundance of mammoths, woolly rhinos and bison. A key factor, Flannery concludes, is the frozen peat and high acidity make it hard for phospherous and nitrgoen hard for plants to access, but when the mammoth in particular roamed "a copious flow of urine and mammoth droppings provided large volumes of the nutrients at the surface", and by eating the vegetation so that it didn't become peat, they reduced acidity. And, Flannery points out, in the last of the Milankovitch cycles, in which the levels of carbon dioxide in the atmosphere fluctuate, some 15,000 years ago, the high was some 15 parts per million of what might have been expected (at 265ppm), it is possible that the rising levels of peat, with its trapped carbon, from plants no longer eaten by the giant grazing animals we'd killed, played a part.
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